Re: Dry method brake fluid exchange and minimum fluid level

First, it's been a long time since I have been here. My bad and "HI" to all.

Now on to my question. I'm doing a brake fluid exchange ointment my 2016 GT4 and, having had a bad experience once with corroded fluid, prefer for safety to use the "dry" method in which the Motive only pressurizes the reservoir, it does not push fluid in. The fluid comes from the reservoir and must be topped up periodically.

It's that period I'm trying to ascertain. In my 986s there is a large space above the "MIN" mark - close to 400mL I would estimate,. In thge 981 not so, the MIN mark is very near the top (or appears so).

How low can I go without danger of introducing air. It will obviously be full when I am done.

TIA,

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

There is a max line. There is also a MIN line. With a flashlight I looked for anywhere that air could get in below the MIN line and the first one I found ( mot clear what it is) is a line running through the firewall toward the pedal assembly or dash. I dont want to flirt with this, so above that is the mold line where the reservoir goes from wide and "squares" to narrower and more irregular. I chose to use that as my cut off point. It seems that I can therefore drive > 300mL through on one fill. Not awful.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

When you are pressure bleeding the system, the reservoir is level or close to it and there are no g-forces acting on the fluid. This gives you more margin for a safe low fluid level than when you're driving.

If you fill the reservoir to the top (above the max line) and bleed down to at or near the min line you should be able to bleed the whole system with only one top off.

Hi Grant. Long time!

But, why?
I don't understand the "dry" approach.
It introduces the chance of drawing air that won't be visible.
It also exposes the new fluid to more opportunity to draw in humidity and chances to spill fluid outside the reservoir.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 313,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Hi Pedro, indeed too long. While I know those risks exist I think they are small, and I had an actual case of contamination (not sure if it was dirt or moisture) in my brake fluid. The only two possible sources were a) form the factory (unlikely) or b) from the motive, so I am gun shy. I recently bought some cheap brake fluid to thoroughly run through the clean the motive of any debris - including the line which is where I suspect moisture could accumulate. From where? Extreme moisture during spring rains in the garage, then condensing.

Thanks, I do agree with all the downsides you list, they jsut pale compared to what occurred to me once. Entering WGI turn 1 with no brakes is not fun.

Grant

gee-lenahan-at-gee-mail-dot-com

... is due to the very aggressive hygroscopic nature of the fluid itself.
It is so thirsty, that it will pull water molecules from the air through the brake likes themselves.
So, many times people think they had contamination from an external source, when they didn't.
That is the reason brake fluid in our cars needs to be flushed every 2 year regardless of miles driven.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 313,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

I do understand that, but in this case clearly no.

All was well. I change my fluid with 600/660 every year. (have to as you know0.

I have never even come close to(from feel) to a soft brake pedal.

Changed fluid before. trip to WGI. Used wet method. After a couple laps pedal got soft nd within a lap went to the floor before turn 1. A pump or 3 got me safely through, but this was absolutely fresh brake fluid. I had done ~ 6 track days on the old (newly 9 months) (but bled) fluid with never an issue.

Repeated bleedings on site did nothing

Came home, ran 2 liters of cheap-O fluid through the system to clean it out; put in new 660. problem solved.

Was it contamination from water in the motive's line?Maybe. Some other contaminant? Maybe.
But it made me very cautious.

In a wet environment condensation can wreck havoc. In the bottle it invisible. In the one (in my case a replaced motive hose, which is I believe fuel line and opaque) it is not.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com